Sodium hypochlorite is a common source of chlorine used for disinfection of drinking water. Low strength solutions of sodium hypochlorite may be produced on site by the electrolysis of brine (NaCl) solutions (less than 1% available chlorine).2Cl−→Cl2+2e− Anode2H2O+2e−→H2+2OH− CathodeCl2+OH−→OCl−+Cl−+H+ Overall reaction
The overall reaction produces hypochlorite (OCl−) which then combines with sodium from the brine to produce sodium hypochlorite.
Side reactions are possible during the process. In particular, some of the hypochlorite that is produced will be further oxidized at the anode to produce chlorate (ClO3−).6OCl−+3H2O→2ClO3−+4Cl−+6H+1.5O2+6e−Additionally, decomposition due to storage and heat can lead to further chlorate production.2HOCl+OCl−→ClO3−+2Cl−+2H−
Recently, chlorate has become a focus in the drinking water industry. In particular, the World Health Organization has issued a guideline which limits chlorate to 0.7 mg/l. In order to keep within this limit, users of sodium hypochlorite are increasingly aware of the importance of knowing the initial levels of chlorate.